poj----1330Nearest Common Ancestors（简单LCA)

题目连接  http://poj.org/problem?id=1330

就是构建一棵树，然后问你两个节点之间最近的公共父节点是谁？

代码：

 /*Source Code
 Problem: 1330        User: huifeidmeng
 Memory: 1232K        Time: 63MS
 Language: C++        Result: Accepted

     Source Code
 */
     #include<iostream>
     #include<vector>
     #include<cstdio>
     #include<cstring>
     #include<cstdlib>
     using namespace std;
     const int maxn=;
     vector<int> tree[maxn],qus[maxn];
     int rank[maxn],father[maxn];
     bool vis[maxn];
     int rudu[maxn];
     int lroot[maxn];
     void init(int n){
          memset(vis,,sizeof(vis));
          memset(rudu,,sizeof(rudu));
          memset(lroot,,sizeof(lroot));
         for(int i=;i<=n;i++){
             father[i]=i;
             rank[i]=;
             tree[i].clear();
             qus[i].clear();
         }
     }
     int find(int a){
        while(a!=father[a])
              a=father[a];
         return a;
     }
     void Union(int a,int b)
     {
         int x=find(a);
         int y=find(b);
         if(x==y) return ;
         if(rank[x]<rank[y]){
           rank[y]+=rank[x];
           father[x]=y;
         }
         else {
          rank[x]+=rank[y];
          father[y]=x;
         }
     }
     void LCA(int u)
     {
       lroot[u]=u;
       int len=tree[u].size();
       for(int i=;i<len;i++){
           LCA(tree[u][i]);
           Union(u,tree[u][i]);
           lroot[find(u)]=u;
       }
       vis[u]=;
       int ss=qus[u].size();
       for(int i=;i<ss;i++){
             if(vis[qus[u][i]]){
                 printf("%d\n",lroot[find(qus[u][i])]);
                 return ;
             }
       }
     }
     int main()
     {
       int cas,n,u1,u2;
       //freopen("test.in","r",stdin);
       scanf("%d",&cas);
       while(cas--){
           scanf("%d",&n);
           init(n);
           for(int i=;i<n;i++){
           scanf("%d%d",&u1,&u2);
           tree[u1].push_back(u2);
           rudu[u2]++;
           }
           scanf("%d%d",&u1,&u2);
           qus[u1].push_back(u2);
           qus[u2].push_back(u1);
           for(int i=;i<=n;i++){
          if(==rudu[i]){ //找到root
            LCA(i);
            break;
           }
           }
       }
     return ;
     }